1. Field of the Invention
The present invention relates to differential drives generally, and more particularly, relates to a hydraulically controlled torque transfer device for use with a differential drive in a vehicle.
2. Description of Related Art
The differential drive is well known in the motor vehicle industry. The differential drive is used in conjunction with the transmission and drive shaft or propeller shaft to turn the automotive vehicle wheels at different speeds when the vehicle is going around a curve, to differentiate the speed of each wheel individually and to provide the proper amount of torque to each wheel in slipping, turning, or other road to wheel conditions.
In a common all wheel drive power train layout of a motor vehicle there is a primary driven front/rear axle and a secondary driven hang on axle that is connected via a prop shaft or drive shaft and a torque transfer coupling to the primary driven axle. The torque transfer coupling is usually directly in front of the secondary driven axle. The axle differential creates the division of power or torque to each side shaft of the axle. The primary driven axle also includes a differential which divides necessary power to the side shaft of each axle and then the wheels. The division of torque between the front and rear axles is completed by the torque transfer coupling which is a separate unit on the drive train system and requires space for its housing and other related parts. There are many different ways to provide torque transfer between the primary driven and the secondary driven axles.
The current state of the art includes friction clutch pack systems that use ball ramp mechanisms and also hydraulic or pump systems. A state of the art pump system utilizes two gear pumps arranged in a static housing one is running with primary axle speed and the other with secondary axle speed in a closed hydraulic circuit wherein each of the gear pumps feed each other. Another state of the art gear rotor pump system is based on a single gear pump. The above mentioned two gear pumps and single gear pumps tend to have difficulties in feeding and externally controlling the rotating pump and they are very complex and expensive to manufacture and seal.
Therefore, there is a need in the art for a hydraulically controlled pump based system for torque transfer control between a primary driven axle and a secondary driven axle in an all wheel drive vehicle. This new hydraulic torque transfer device should combine the simplicity of a single gear rotary pump (gerotor pump) with the advantage of a more complex two pump system that has a stationary hydraulic circuit.